1. Field of the Invention
The present invention relates to a process and related plant for manufacturing steel plates without interruption from the continuous casting to the last rolling stand.
2. Description of Related Art
It is known that traditionally, in this field of manufacturing, “reversible” rolling stands have been generally used to roll, by means of several longitudinal and transversal passes, in order to increase each time the product size in length and width, an ingot, preferably of rectangular cross-section, or a slab suitably heated upstream in a heating and temperature equalization furnace, until obtaining a plate of desired thickness and width. The dimensions of the ingot or slab, the latter being possibly produced from continuous casting, are such to show a thickness between 120 and 400 mm and a width between 1000 and 2000 mm according to the type of steel and the technology employed for the manufacturing.
It is also known that in this type of processing the ratio between the thickness of the starting material, i.e. the ingot or slab, and of the desired final plate should not be less than 1:4 in order to ensure welding of possible pores present in the core or middle zone, which are typical in ingots/slabs of great thickness. This means, for a plate having final thickness of 50 mm, an initial slab with minimum thickness of 200 mm.
With the subsequent development of the thin-medium thickness slab technology, plants have been designed by which slabs with a thickness of up to 150 mm are cast, having a width of up to 3600 mm. These slabs are subsequently cut and, upon passing through a heating and temperature equalization furnace, are forwarded in line to a reversible rolling mill which however is adapted to longitudinally rolling only.
With these plants the thickness ratio between slab and final plate can be as low as 1:3, whereby a minimum slab thickness of 150 mm would be required for a plate 50 mm thick. Of course it is also possible with these plants to produce not only plates but also strips wound in coils by making the same reversible stand to work with two rails in a furnace (“plate/Steckel mill technology”). It is clear that with a reduction ratio 1:3 between slab and final plate, to obtain thicknesses of 40-50 mm for the finished plate it is necessary that slabs of 120-150 mm are cast at a maximum speed in the order of 2 m/min, that is insufficient for an in-line rolling process without interruption, requiring on the contrary a minimum speed of 3.5 m/min.
These considerations have prevented so far from adopting in the plate manufacturing the “cast-rolling” technology already known for manufacturing strips. From experimental tests, that however have not made possible to obtain reductions higher than 35% owing to the reduced torque value of the rolling stands, mathematic simulating models have been developed. It has been understood from these models that the same quality results can be reached with a reduction coefficients even greater than 50% and even up to 60%, bringing to more compact plants and further reducing the production costs and investments.